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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 147 (1996), S. 729-744 
    ISSN: 1420-9136
    Keywords: Volcanic tremor ; intermittency ; chaos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Harmonic tremor is widely studied and modelled in a very narrow frequency band (1–5 Hz) which represents the eigenfrequencies of a resonator assumed as the source of the phenomenon. Minimal effort was dedicated towards understanding its behaviour in larger temporal scales. Here we characterise the dynamic behaviour of volcanic tremor while evaluating the complete spectrum of the generalised dimension of the phase space. The starting time series constitutes the tremor amplitude picked every 10 minutes. The choice of this lag time is made on the basis of a qualitative analysis of the properties of the tremor. The results show intermittent behaviour of the dynamics which requires an 8-dimensional map to be completely described. An interesting result is that the maximum clustering of point density in phase space occurs in a monodimensional space which implies a periodicity sometimes observed experimentally. An appropriate predictive model needs more constraints on the nature of the eight variables involved in the process.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 97 (1989), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Results of studies concerning seismic activity (earthquakes and tremor) and its relation with eruptive events on Mt Etna are briefly discussed.Seismic records collected from 1977 up to 1986 have been analysed and special care was given to observation of changes in some seismic parameters, such as the rate of microseismic activity, the amplitude and dominant spectral peaks of the volcanic tremor, which vary significantly in relation to the occurrence of eruptive events.The systematic nature of variations in the seismic parameters considered allows us to propose a preliminary model which puts all the observations made so far into a wide context giving an interpretative hypothesis of the magma uprise mechanisms preceding either summit or flank eruptions.Summit eruptions are modelled in two stages and occur without changes in the seismic parameters considered, except for a sharp increase in tremor amplitude almost coincident in time with the eruption onset.Flank eruptions are modelled in three stages and follow a simultaneous change of all the mentioned parameters with time. the onset of these eruptions is in fact preceded by an increase in both the daily number of shocks and the amplitude of the volcanic tremor as well as a shifting from relatively high values in the dominant peaks of the tremor spectra, which appear in the pre-eruptive stage, towards usual lower frequency values (1.0–2.3 Hz).
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0819
    Keywords: Mt. Etna Italy Earthquakes Seismic strain Stress inversion Volcanic processes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract. Kostrov's (1974) algorithm for seismic-strain tensor computations, in the version implemented by Wyss et al. (1992a) for error estimates, has been applied to shear-type earthquakes occurring beneath the Etna volcano during 1990–1996. Space–time variations of strain orientations and amplitudes have been examined jointly with ground-deformation and gravimetric data collected in the same period and reported in the literature. Taking also into account the information available from volcanological observations and structural geology, we propose a model assuming that hydraulic pressure by magma emplaced in nearly north–south vertical structures produces the E–W orientation of the maximum compressive strain found in the upper 10 km beneath the crater area. In contrast, regional tectonics deriving from the slow, north–south convergence between the African and European plates appear to play a dominant role in the generation of stress and strain fields at crustal depths deeper than 10 km below the volcano. According to our interpretation, the progressive ascent of magma through the upper crust prior to eruption produces the observed gravity changes, cone inflation and unusual seismic strain rate in the upper 10 km associated with a more sharply defined seismic deformation regime (i.e. very small confidence limits of the ε1 orientation). In agreement with this model, deflation revealed by ground-deformation data during the course of the major 1991–1993 eruption was accompanied by a practically nil level of shallow seismicity.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 70 (1985), S. 234-239 
    ISSN: 1432-2242
    Keywords: Maize ; Repetitive DNA ; A and B chromosomes ; Centromere activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Clones from a family of highly repeated sequences present in a heterochromatin rich maize line have been characterized by sequencing and chromosome location. The repeats differ from each other in length and degree of sequence homology, and show areas rich in purine and pyrimidine. In “situ” hybridization experiments indicate that the repeats are mainly located in the knob heterochromatin of the A chromosomes and the centromeric heterochromatin of the B chromosome. However, in addition to previously published data, some copies are also distributed in euchromatic regions of the A chromosomes and in the distal heterochromatic block of the B chromosome. The results are discussed in relation to the centromeric activity of maize heterochromatin.
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  • 5
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Sister chromatid exchange (SCE) induction by methotrexate (MTX) was analyzed in C3H10T1/2 clone 8 mouse cells and in two MTX-resistant subclones with numerous double minute chromosomes (DM) present in the majority of cells. Significantly higher SCE levels were found, as expected, in sensitive cells after treatments with 10-2 or 10-5M MTX but not in resistant cells permanently growing in the presence of a high concentration of MTX (2×10-3M) and characterized by a markedly lower cell cycle replication index (R.I.), i.e. in conditions that are known to otherwise favour SCE induction. These observations suggest, for the MTX-resistant cells under study, the existence of conditions limiting SCE formation.
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  • 6
    Publication Date: 1990-03-01
    Print ISSN: 0016-6707
    Electronic ISSN: 1573-6857
    Topics: Biology
    Published by Springer
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  • 7
    Publication Date: 1995-07-01
    Description: Juvenile chronic myelocytic leukemia (JCML) is a rare disorder of early childhood. Characteristic of JCML are the progressive appearance of high levels of fetal hemoglobin (HbF), reflecting a true reversion to a fetal type of erythropoiesis, and the presence of colony-forming cells able to grow in vitro spontaneously in the absence of growth factors. To better understand the relationship between the erythroid abnormalities and the leukemic process, we analyzed the expression pattern of specific genes related to erythroid differentiation--GATA-1, EPOR, alpha-globin, beta-globin, and gamma-globin genes--in JCML peripheral blood (PB) cells and in vitro-derived colonies. Northern blot analysis of PB cells from five JCML patients indicated levels of GATA-1 transcripts much higher than those usually found in other types of leukemic cells, and S1 nuclease protection assay detected significantly increased expression of gamma-globin mRNA. Reverse transcription-polymerase chain reaction (RT-PCR) analysis of single granulocyte-macrophage colony-forming unit (CFU-GM) colonies, obtained in vitro in the absence of added growth factors from four JCML patients, detected GATA-1, EPOR, and globin (alpha and gamma) transcripts in most of the colonies tested, in contrast with control CFU-GM from normal bone marrow, which were positive only for GATA-1. Single JCML colonies were tested for the presence of two different transcripts; whereas alpha- and gamma-globin genes appeared mostly coexpressed, beta-globin mRNA was detected only in a minority of the gamma-globin-positive colonies, indicating that the leukemic pattern of hemoglobin synthesis is mainly fetal. In addition, the leukemic cells occurring during blast crisis of one of our patients displayed the typical features of a stem cell leukemia (CD34+, CD19-, CD2-, myeloperoxidase-). In this sorted CD34+ population, we detected the presence of a marker chromosome, der(12)t(3;12), previously identified in bone marrow cells at diagnosis and an expression pattern superimposable to that of the JCML colonies, consistently displaying a high gamma-globin:beta-globin mRNA ratio. The expression of erythroid markers within populations of leukemic cells, both in vivo and in vitro, supports the hypothesis that abnormal JCML erythroid cells may originate from the same mutated progenitor that sustains the growth of the leukemic cells.
    Print ISSN: 0006-4971
    Electronic ISSN: 1528-0020
    Topics: Biology , Medicine
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  • 8
    Publication Date: 1991-05-01
    Description: We identified seven new recurring translocations among 483 cases of acute lymphoblastic leukemia (ALL) with adequate chromosome banding studies. Four were apparently balanced [t(1;3)(p34;p21), t(7;9)(p15;p23- p24), t(12;13)(p13;q14), t(17;19)(q22;p13)], while three were unbalanced with the formation of a dicentric chromosome [dic(7;9)(p13;p11), dic(7;12)(p11;p12), and dic(12;17)(p11;p11-p12)]. One translocation was observed in five cases, two in four cases, and the remaining four in two cases each. The modal chromosome numbers in these 21 cases were 45 (n = 11), 46 (n = 8), and 47 (n = 2). Eight of the 11 cases with a dicentric chromosome had a modal number of 45. Only a single translocation was found in 14 cases (67%), representing the sole structural abnormality in six cases. In three of the seven translocation subgroups, the blast cells were consistently of B lineage (pre-B, early pre-B, or both); in all others, they represented both the B and T lineages. The small size of these subgroups prevented definitive clinical correlations, although it may be important that two of the four cases with a t(17;19) and an early pre-B-cell immunophenotype had disseminated intravascular coagulation, an event usually observed in acute promyelocytic leukemia or T-cell ALL. These findings add substantially to the existing list of nonrandom chromosomal translocations in childhood ALL and may help to explain the genetic alterations leading to the loss of normal growth control mechanisms in this disease.
    Print ISSN: 0006-4971
    Electronic ISSN: 1528-0020
    Topics: Biology , Medicine
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  • 9
    Publication Date: 1991-05-01
    Description: We identified seven new recurring translocations among 483 cases of acute lymphoblastic leukemia (ALL) with adequate chromosome banding studies. Four were apparently balanced [t(1;3)(p34;p21), t(7;9)(p15;p23- p24), t(12;13)(p13;q14), t(17;19)(q22;p13)], while three were unbalanced with the formation of a dicentric chromosome [dic(7;9)(p13;p11), dic(7;12)(p11;p12), and dic(12;17)(p11;p11-p12)]. One translocation was observed in five cases, two in four cases, and the remaining four in two cases each. The modal chromosome numbers in these 21 cases were 45 (n = 11), 46 (n = 8), and 47 (n = 2). Eight of the 11 cases with a dicentric chromosome had a modal number of 45. Only a single translocation was found in 14 cases (67%), representing the sole structural abnormality in six cases. In three of the seven translocation subgroups, the blast cells were consistently of B lineage (pre-B, early pre-B, or both); in all others, they represented both the B and T lineages. The small size of these subgroups prevented definitive clinical correlations, although it may be important that two of the four cases with a t(17;19) and an early pre-B-cell immunophenotype had disseminated intravascular coagulation, an event usually observed in acute promyelocytic leukemia or T-cell ALL. These findings add substantially to the existing list of nonrandom chromosomal translocations in childhood ALL and may help to explain the genetic alterations leading to the loss of normal growth control mechanisms in this disease.
    Print ISSN: 0006-4971
    Electronic ISSN: 1528-0020
    Topics: Biology , Medicine
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  • 10
    Publication Date: 1992-04-01
    Description: The prognostically important 1;19 chromosomal translocation can alter the E2A gene on chromosome 19p13 in childhood B-cell precursor acute lymphoblastic leukemia (ALL), leading to formation of a fusion gene (E2A-PBX1) that encodes a hybrid transcription factor with oncogenic potential. It is not known whether this molecular alteration is a uniform consequence of the t(1;19) or is restricted to translocation events within specific immunologic subtypes of the disease. Therefore, we studied leukemic cells from 25 cases of B-cell precursor ALL, with or without evidence of cytoplasmic Ig mu heavy chains (cIg); 17 cases had the t(1;19) by cytogenetic analysis. Leukemic cell DNA samples were analyzed by Southern blotting to detect alterations within the E2A genomic locus; a polymerase chain reaction assay was used to identify expression of chimeric E2A-pbx1 transcripts in leukemic cell RNA; and immunoblotting with anti-Pbx1 antibodies was used to detect hybrid E2A- Pbx1 proteins. Of 11 cases of cIg+ ALL with the t(1;19), 10 had E2A- pbx1 chimeric transcripts with identical junctions and a characteristic set of E2A-Pbx1 hybrid proteins. Each of these cases had E2A gene rearrangements, including the one in which fusion transcripts were not detected. By contrast, none of the six cases of t(1;19)-positive, cIg- ALL had evidence of rearranged E2A genomic restriction fragments, detectable E2A-pbx1 chimeric transcripts, or hybrid E2A-Pbx1 proteins. Typical chimeric E2A-pbx1 transcripts and proteins were detected in one of eight cIg+ leukemias in which the t(1;19) was not identified by cytogenetic analysis, emphasizing the increased sensitivity of molecular analysis for detection of this abnormality. We conclude that the molecular breakpoints in cases of cIg- B-cell precursor ALL with the t(1;19) differ from those in cIg+ cases with this translocation. Leukemias that express hybrid oncoproteins such as E2A-Pbx1 or Bcr-Abl have had a poor prognosis in most studies. Thus, molecular techniques to detect fusion genes and their aberrant products should allow more timely and appropriate treatment of these aggressive subtypes of the disease.
    Print ISSN: 0006-4971
    Electronic ISSN: 1528-0020
    Topics: Biology , Medicine
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